If one splits a clip by mistake is there a way to put it back together again and remove the split?

if you can't use the UNDO.. just drag the right side of the cutted clip to add new frames (from original clip)

I was not clear. What I mean is to remove a split and make the clip whole again.

Make this.
https://1drv.ms/i/s!Arsv9-Zh1TgPlHkyNkA4qHITdDHw

Into this.
https://1drv.ms/i/s!Arsv9-Zh1TgPlHqzJLy4WxumZiZf

yep, delete the 2nd part of the clip...
and after that drag the right side of the first part.. increasing again the size of the clip. (maybe take a look at the frame number to identify exactly when to stop to "enlarge" first part)