I haven't done the CGK turnaround on LH but have done on SQ many, many times.
If you already have your onward BP (recommended) on arrival in CGK simply go up the escalator or stairs just before immigration to departures level (you may or may not get rescreened). The departure tax of 100,000 rph (or equivalent in major currency) is payable at the gate. No need to clear immigration or visa on arrival. 1:15 is ample time to turn around.
If you do not have onward boarding pass then need to visit the transfer desk on the lower level before immigration. They may be able to issue there or may need to escort you through immigration to landside check in.