Can't get rubber stopper back into Contigo Kids cup lid

Can't get rubber stopper back into Contigo Kids cup lid

I removed the rubber stopper (not sure what the right term is for it but it looks like a mini nipple) from the Contigo kids cup lid to clean it, and now I…

Contigo® Kids Spill-Proof Tumbler with Straw, 14oz

Can't get rubber stopper back into Contigo Kids cup lid. Suggestions?

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