I am no expert, but on my 1972 Peugot I remove the cotterless cranks. Next I take off the lock ring on the side (LH) opposite the chainwheel and spin out the cup that holds the bearings. Now I can remove the crank. That leaves the cup on the RH side accessible to me by putting my finger in the hole left by the crankshaft.

I usually stick a long screwdriver in the bracket to knock the BBs out the hole and catch them on a coffee can lid. I clean out the cup to remove all the old grease and sometimes I scrub it with some #000 steel wool. I replace the grease by putting about 1/2" strip on my finger and then just slip it up and into the cup - repeating all around. The BBs will go in one at a time and the grease holds them in place until I drop the crank back down of top of them.

The LH cup is in my hand and I just lay in a little grease and them smooth it around the entire surface, placing the BBs in next. I then put the cup back on and then the lock ring. I just "feel" for the play until there is no play and the crank spins easily. I tighten the lock ring and check again. Occasionally tightening down the lock ring snugs the cup too much and I have to back it out and try again.

I realize your bike has cottered cranks but the basics are not too different I am confident.