Merging Cells

If iOS, select the cells, tap Cell Actions... in the bar the pops up, tap Merge Cells.

IF macOS, select the cells, choose Table > Merge Cells from the menu.

SG

If you are referring to the iOS version of Numbers (which is what your signature hints at), you should ask this in the iWork for iOS forum. For the Mac OS version of Numbers, merging cells has not changed. I do not know about the iOS version.