how to adjust T4 for missing boxes

Hello lindageb,

Welcome to the Community. I'll be glad to share more information about adjusting T4s for the missing boxes you've mentioned above. 

It's important to note that entries for Box 50 - RPP or DPSP registration number and Box 52 - Pension adjustment are not supported in QuickBooks Online Payroll. If you need to add these to your employee’s T4, you will need to manually fill out and submit the T4 or use software such as ProTax (FX) or ProFile FX to create and file the T4s.

To add to the above, here's a helpful article that shows you: How to manually fill out and submit the T4. I'll be happy to answer any questions in the comments below. Feel free to ask.