It depends on where you stored your custom template. The templates that SAS ships are stored in the template store SASHELP.TMPLMST. It's unlikely you have write-access to the SASHELP library, so the original crosstabs template is still there. Probably your custom template is stored in SASUSER.TEMPLAT. If that's the case, deleting your custom template from SASUSER.TEMPLAT will let you go back to using the original version.
If your custom crosstabs template is the only template in SASUSER.TEMPLAT, just delete the entire template store. If there are templates other than that one in SASUSER.TEMPLAT, and you want to keep them, you'll need to use
PROC TEMPLATE to delete just the crosstabs template. You should probably
contact Tech. Support for more help.
If you have actually replaced the original crosstabs template in SASHELP.LIBRARY with your own, you'll have to re-install the original templates. You'll definitely have to contact Tech. Support.