Welcome to the board. Most of our old beasties are fairly simple and will respond well to basic maintenance even without a manual A warm hair dryer can melt out old grease or oil. Open up the faceplate and oil everything that moves ( or should move) gently wiggle at the zig zag movement bits. .The revers button is harder to lube. If you can open the top of the machine it is easier to oil. Otherwise oil from other angles.
I proposed to my girlfriend on a sail boat. The rigging had broken and the sail wouldn't lift . I said,
"The sail won't work, I have the oar and the rudder and it's a long way to shore. Will you marry me?" Thankfully she said yes.