It's in!

This is what I did:

Instead of wrapping him in a muslin wrap, I used a really big cot sheet with his arms pinned by his side, not across his chest. I sat on my knees with him between then, so my knees were roughly at his armpits, not squeezing him, just more to get to his face at the right angle. Previously I had been leaning across him, like sitting at his side or leaning over the change table. With my left hand, I lifted his lid and held his forehead at the same time and had the lens in my right hand. When I needed him to look down, I said "Ah boo!" and he looked down toward me. I slipped it up into the top lid then pulled the bottom lid down and it slotted into place. Sounds easy hey lol.

Unwrapped him then lots of cuddles.

RELIEF.

Now we can get on with our day.