When you want to generate a report, Koinly will tell you how much of an impact the missing transaction history will make on your account if you submit it as is, so it’s up to you and your accountant to decide whether that amount is negligible or not. For example in my personal case, it’s $61, now do I want to waste x amount of time fixing this for such a small amount? No. So, go over your account, talk to your accountant, and make that decision after taking everything into consideration.
If you do want to fix the issue and you decide it’s really too much to accept, then take a look at these articles and follow the steps to correct the problem.