Google is having trouble finding a LX M661 crank.
Exactly what is it that you have, and what are you trying to fix?

There's a LX FC-T661 crankset. That's outboard (cartridge) bearings HT II.
Not much there to "open, clean and regrease".
Wipe with cloth, ride until it dies.
Buy new BB bearings. Install. Repeat.

There's an SLX crank. Also HT II. Treat as above.

It's POSSIBLE to replace the bearings ONLY, and keep the bearing cups. But not many bother.

It's also possible to gently pry the seals out and add more grease, which some claim improves bearing life under poor conditions.
Not many bother with that either.

The generation before that used a square taper axle in a sleeve holding cartridge bearings.
Notthing there either to sensibly "open, clean and regrease".
Treat as above.

Only BB standard where "open, clean and regrease" really makes sense is with cup & cone type BBs.