There is no one button press or a click in CPS to reset these radios back to a default state. You will need to read each radio with cps then go to town clearing the codeplugs out. If all your radios have the same model number and feature set you may be able to clear one radio and clone that codeplug to the rest of them to save some time. I've never done cloning before so someone else will have to advise on that.
This advice is good as far as it goes. Having had to do this a number of times, I would add the following, mainly to minimize the hassle you're going to get with errors generated during the process.
Assuming conventional (i.e., no trunked):
Start by creating a new conventional "system." Label it "System 1." Create a new conventional "personality," point it to System 1, and label it "Personality 1." Create a new zone/channel, which will contain a single channel. Leave freqs at the default values and point it to Conv Sys 1. Move this zone to position 1.
Now, and in this order:
Delete all the scan lists. The easy way is to click on scan lists in table mode, highlight all but #1 as a group, and click on delete.
Ditto all the conventional personalities except #1, same way.
Ditto all the conventional systems except #1, the same way.
At this point, you can probably ignore everything else (e.g., menu items), except (if you have one) an MDC alias list.
Trunked:
You do the same but first:
Create a new trunked system. The SysID will be 1 and you won't be able to change it.
Create a new trunked personality, and point it to System 1.
Now delete all trunked personalities but #1, as a group, as above.
Ditto trunked systems.
No need to create a single trunked talkgroup in the zone/channel page.
Hopefully, by the time you finish the above, there won't be any residual errors. (With XTS, errors will bar you from saving the codeplug or writing it to a radio.) If there are errors (e.g., Emergency Revert vectors), just highlight the errors one at a time, double click on the highlight, and it will take you to the error. Usually resetting things to the "factory default" will cure them.
OK, now with the errors gone, save the file to disk and then write the codeplug to the radio you read it from. After this, you should be able to clone all identical radios.
If firmware/feature set differences preclude a clone, you can try the "Top Level Drag and Drop." Frankly, I've had this generate even more errors, sometimes esoteric ones that take a while to figure out. What I do is use the Import/Export function to export the cleaned file, read the next radio, and then import the output of the cleaned export. Be sure to set your Import/Expore option to "overwrite." I have found that Import/Export is smart enough to ignore any source file parameters that are not relevant to the target radio.
Good luck.