The cable inners stretch and the cable outers compress on all new bikes in the first few hours on the road. On all bikes. This throws the gear indexing out. There's a user adjuster on the rear dérailleur to compensate for this:

Turn the bike upside down, operate the shifter and turn the pedals until the chain is on the smallest rear sprocket, then move the selector one click while turning the pedals. The chain should climb onto the second smallest sprocket. No? Turn the adjuster half a turn, go back to small, and repeat until you get smooth shifts onto sprocket #2, but not past it.

Then check all the sprockets, once you have correct shifting to #2, you should have correct shifting all the way up.

If you get it wrong, start on the smallest sprocket again.

Fine tune by listening for rattling noise on the middle sprockets and see if small turns of the adjuster remove it.

There's loads of vids on YouTube to help.

Cheap bikes can run well. Become the mechanic. Buy grease.

* Note for Dahon Neos users - do the adjustments starting with the chain on the largest sprocket, adjust for jump to second largest.