Preserve Tell’s first functioning part of Switzerland (6)
I believe the answer is:
canton
'part of switzerland' is the definition.
(Swiss administrative subdivision)
'preserve tell's first functioning' is the wordplay.
'preserve' becomes 'can' (canning is a kind of preserving).
'first' indicates taking the first letters.
'functioning' becomes 'on' (I've seen this in other clues).
The initial letter of 'tells' is 't'.
'can'+'t'+'on'='CANTON'
(Other definitions for canton that I've seen before include "Administrative subdivision of, eg, Switzerland" , "State of Switzerland" , "Old Chinatown" , "European territory" , "Political region in Switzerland" .)