Hi
When before entering this into cell you formatted the cell as Custom
"[h]:mm", then simply reformat it p.e. as Custom 'd"d "hh:mm'
When your entry is a string, then (let's it be in cell A1) use formula
=TIME((LEFT(A1,FIND(":",A1)-1))*1,(RIGHT(A1,LEN(A1)-FIND(":",A1)))*1,0)
to convert it to time (format the cell with formula like A1 in example
above)