Does anyone have a tip on how to stretch an aftermarket tie rack boot to offside . Its impossible to stretch it all the way round the steering rack end as you cannot get any hands fingers etc to hold the boot on while you similarly slip the rest on over the cup end. Maybe the neck of a plastic bottle , but then will it stretch the small end enough to remove it off the end of the inner tie rack.

Would softening it first using, for example, a bowl of very hot water or a hairdryer work?

Yes that’s a good idea , but it’s quite soft and pliant as it is. It’s getting it to stay on on the part you can get at , then access to the top half is impossible (with my hands anyway)!
I removed the front guard to access that part but run out of patience by then . I’ll have a go tomorrow night with a new look at it . Haha.
Clean it down and lightly glue ?

I don't quite understand your first post. I am assuming you have separated the inner tie rod and tie rod end; slid the boot onto the inner tie rod and are struggling to fit the big end over the steering rack?

When I've done these in the past, at this stage, I've found turning the steering so that whichever side you are doing is pulling the boot together / compresses it helps to stop it pulling off.

Sorry , not explained too well, but yes, that's correct.
The problem lies with stretching it over when you can.only get on hand at the time.
What I did eventually was to stretch the boot over a jubillee clip opened to slightly wider than the rack cup, then placed over it and keeping in place remove jubillee , widen it and bring it back over and clamp the boot ...... tricky but a lot easier.