wanted to thank Mr. B for promoting him (to a better job)

Mr A wanted to thank Mr B for helping him to find a better job.

(Promoting only works if Mr B is Mr A's superior in the same firm, which does not necessarily seem to be the case here.)

Yes. Very good point.

It would also be possible to omit the "to" before "find."

Mr A wanted to thank Mr B for helping him find a better job.

"Promote" würde ich hier sogar definitiv ausschließen, denn dann hätte im OP "befördern" stehen müssen.

#5 Das war jetzt aber mal ein sehr kurzer Beitrag...

Danke!

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In der Kürze liegt manchmal die Würze, California.