If I am stringing and come to a bead with a hole too big, what do I do?

Well, you can tie a larger knot in the string/wire/whatever you are stringing.
You can place a smaller bead on the string. One that will not slip off, but the bead itself is larger than the hole in the other bead.

What exactly is the problem? Is it slipping off the string, or is it too loose, or what?

Well, you can tie a larger knot in the string/wire/whatever you are stringing.
You can place a smaller bead on the string. One that will not slip off, but the bead itself is larger than the hole in the other bead.

What exactly is the problem? Is it slipping off of the string, or is it too loose, or what?

Thank you very much for your reply.

What exactly is the problem? It is slipping off the string

Well, will any of my suggestions help you?
Or, is your project so specific that you cannot tie knots/add extra beads?

At least, you could apply a small amount of glue to the string, and leave the bead there to dry. However, this will be permanent in case you don't want it to be, and it may not look very professional.

Thank you for your great answer. I appreciate a lot your kind help.