Where to enter severance payment in self assessment form when auto populated online in P45 pay

I left my previous job with a severance package, and completing my self assessment, I expected to enter this package in the “Other tax reliefs” section. However, normal salary and severance payment are already entered online in one amount, which is shown when I start to enter the tax return in “Information HMRC holds about me.” As “Pay from xxx - total from your P45 or P60. Enter the amount before tax taken off”. However, my P45 does not contain the severance payment, only the normal salary. Which I believe is correct. I don’t understand what to do. Do I leave this as it is, and not fill in “other tax reliefs”? Or do I correct the “Pay from xxx - total from your P45 or P60. Enter the amount before tax taken off” to the normal salary shown on my P45, and fill in the severance payment in the “other tax reliefs”? I've see contradicting advice on this forum since it seems the tax treatment would be slightly different for either scenario, and it's difficult to get hold of anyone IRL.

Hi lk24,
Please see:
Additional information notes
Thank you.