Can I return a assembled bike to a Walmart store?

The logical thing would be to ask Walmart.

Ask Walmart. Check their returns policy. Check what you signed up to when you ordered the bike. Sounds like you just made a bad buying decision. Next time do try, try, try BEFORE (BEFORE) you buy. 

I guess CALLING your local store & asking is out of the question.  Just way too logical.  Or looking at Walmart's return policy which is CLEALY posted on their website - also out of the question.  https://www.walmart.com/help/channel/returns-repla...  

Oh...one more thing.  You didn't buy a bike from Walmart.  You bought a BSO (bicycle shaped object).  The worst possible parts & components on the planet.  Plus you can't TEST RIDE any of them before the sale.  You can do that at a REAL bicycle shop.  But, oh no...you had to save a few dollars by going cheap.  Learn anything? 🤔  Shop small.  Shop local.  Support your local bike shop - not some multi-billion dollar conglomerate.   

You must return it just as you received it..

What would WalMart do with a used bike?  They can't sell it - so a 100% loss because you don't like what you bought?

Really . . . I don't know if a store manager has the authority to take on a loss . . . or how much noise you would have to make.  Were it me, I would try to sell someplace like Craigslist - or even donate it to a charity store or give to a needy kid.