Just reheat the soldered spots and scrap the soft solder away with a wooden/ metal tool...
You will probably find some marks/ recesses around the soldered areas, which will remain visible even after reblueing.
Once you removed most of or all solder, sand it to get rid off every remaining bit of solder...it won´t blue!
Give the scope body some passes with steelwool and degrease it before applying any blueing compound...I recommend to sand the whole body, so the reblued areas "blend" with the rest of the scope.
Have used cold-blueing AND heat-blueing in the past, depending on what chemicals I had on hand at the time. BOTH methods work good on the Hensoldt steel body.