I'm not sure where you are at, but if you want to edit input, you need to be able to:
1) Place it (the string) back on the line.
2) Use the INKEY$ routine to edit it.
I simply feed the variable back into the routine and it is ready to work with. This is yst another one of my many reasons I feel intermediate to advanced programmers should abandon INPUT and use INKEY.
P.S. I like the Input entry fields that Mac created. I use many such editible fields fields in my business apps. They are very concise and efficient to use.