How do you make already-cooked beef stew meat more tender?

my guess is its too late

10 hours is much too long, even in a crock pot on low.

Believe it or not, meat can dry out while cooking in liquid.

For this batch, not much you can do... cut the meat into smaller bits.

What cut of beef did you use?

For the future, my suggestion is to cook for 6 to 8 hours.

A good cut of beef to use is a chuck roast (better marbling). The round, brisket and rump seem to dry out a lot quicker than the chuck.

Next time cook on high heat for 6 hours. That works for me.

10 hours is the minimum cooking on low. Next time, cook for 10-14 hours.

kinda shred the meat , add a bit more water to the gravy and and set it on low in your crock pot to rehydrate the meat . if left in it bulk form it will not absorb the fluids. next time look for more marbling ( thready fat ) in the meat itself.

Too late. Next time use a brisket.