Take a hike from bottom of Mongolia into Tibet, somehow (4,2)
I believe the answer is:
beat it
'take a hike' is the definition.
(both can be used to tell someone to go away)
'bottom of mongolia into tibet somehow' is the wordplay.
'bottom of' says to take the final letters.
'into' means one lot of letters goes inside another.
'somehow' indicates anagramming the letters.
The final letter of 'mongolia' is 'a'.
'tibet' is an anagram of 'betit'.
'a' inserted inside 'betit' is 'BEAT IT'.
'from' acts as a link.
(Other definitions for beat it that I've seen before include "Scram, take a powder" , "Make off hastily" , "try out drum kit?" , "Sling your hook!" , "Scarper" .)