Hard time getting back into Prague ground to assemble, as in former days (8)

'assemble as in former days' is the definition.
(old-fashioned term meaning to assemble)

'hard time getting back into prague ground' is the wordplay.
'hard time getting' becomes 'ht' (I can't explain this - if you can you should believe this answer much more).
'back' shows that the letters should be reversed in order.
'into' indicates putting letters inside.
'ground' indicates anagramming the letters (grind the letters ).
'ht' written backwards gives 'th'.
'prague' is an anagram of 'upgaer'.
'th' placed into 'upgaer' is 'UPGATHER'.

'to' is the link.