Bikes on trains in the UK

Last time I did it in late 2020, you basically had to wait for the platform to be announced, then rush to get on with enough time to work out where you were meant to put your bike. Then put it in to the tiny little rack. I'm not aware of any way of getting earlier access to the platform.
If you can do some homework before and work out which carriage you are likely to be aiming for, it reduces the stress levels a bit.
Also, think about what you'll do with your luggage while you are putting your bike on - leave on platform or carry with you, if not too many small bags to manage. You can leave things like frame bags on, but best to take most off as may well be in the way of other bikes / bits of train.
Good luck!

Bike carriages on Avanti are normally at the end (generally at the far end, coach A). As above, I don't know any way of finding out in advance which platform the train will be (although I guess you could go old fashioned and just ask someone) but it's normally up 10-15 minutes in advance.

You then need to try and find someone to actually open it if it isn't already open. Also worth reminding the train manager that you have a bike on and will be getting off at Preston.

At Preston you then jump off and attempt to find some bugger to open the bike carriage door so your bike doesn't carry on to Glasgow. You may have to stick your foot in the door to stop the train setting off if worst comes to worst.

For Preston to Blackburn there's no booking. There is a bike carriage with a bit of extra space but unless the train is packed then you're probably OK in any vestibule as it is only one stop (assuming you are on the fast train).

Get there a bit earlier than usual (half an hour is fine) and try and find a staff member on the platform, they often know which end of the train the bike carriage will be.