I just mailed my full citizenship application 3 days ago on March 25th (Wednesday), but I realized now that I forgot to include some of my absences back in 2015 (I had a 4-month work term in UK and a 1 week vacation in Cuba). With this correction and additional absences, my eligibility and total physical presence remains unchanged at 1,106 and I am still eligible to apply. What should I do now? How should I contact them to provide them with a new piece of Physical Presence Calculator with those corrections and my signature? Any advice is greatly appreciated, thank you all.
Assuming you are correct, that there is NO change in the total calculation of days present in Canada (which, frankly, does NOT make sense; addressed more below) . . .
There is little or nothing you can do until AOR and you have a file number for this application. Once you have that, you can mail a correction (with explanation, keeping it very brief) referencing the file number, or (I believe) use the webform access to update this information (others here are far more familiar than I am with this procedure).
Or you can wait until scheduled for the interview (probably no sooner than sometime in 2021, given the current situation), and be prepared to offer the correct information during the interview. Either proactively or waiting until asked.
Generally, if the information has no impact on the physical presence calculation outcome (number of days credited toward meeting the presence requirement), and thus cannot have any impact on whether the applicant is qualified, and is not otherwise misleading, there is NO rush to make corrections. IRCC realizes applicants make mistakes, and mistakes of little or no import generally cause no problems. Applicants should be prepared to correct and explain the mistake, especially so if asked, but mistakes not directly related to qualifying elements rarely trigger problems.
THAT SAID . . . it is NOT clear how it is, given 130 or so days additionally absent from Canada during your eligibility period, that your "eligibility and total physical presence remains unchanged at 1,106." DOES NOT ADD UP.
If you did not report having residence status in Canada during that period of time, in 2015, so that in the presence calculation you submitted there was NO credit for being IN Canada those days in 2015, then correcting the travel history would not affect the total.
The way you have described the situation, however, indicates you did have residence status, and was in Canada, back in 2015, and in your presence calculation you reported this period of time as days IN Canada. You did not report approximately 130 days absence during that time. In which event, if you otherwise correctly and completely entered information in the online physical presence calculator, except failing to report the times you were absent (approximately 130 days), for that time period the calculator output would have given you credit for approximately 65 days (pre-PR days counting as half-days) toward the presence requirement. Now, reporting those days as days absent should, thus, change the total output calculation by subtracting the credit of 65 days.
CHANGING the total physical presence calculation. Reducing it by 65 days.
OVERALL --
I will not attempt to guess what your situation actually is. You report that even after including the absences in 2015, that the total presence calculation remains unchanged and is still above the 1095 day minimum. If you are correct about this, there should not be a problem. Once you get AOR you can make the correction.
BUT if the calculation you submitted with the application included pre-PR credit for days you were in Canada in 2015, this will change the total. And in that event, there are other aspects of this to consider and address.