The original story said “lifting a de facto ban on American military contractors deploying to Ukraine, four US officials familiar with the matter told CNN, to help the country’s military maintain and repair US-provided weapons systems”.
If this is a policy that Biden created through executive order, then he can reverse the policy.
If this is legislation, then Congress will have to pass legislation rescinding the ban & Biden will have to sign the legislation.
There are situations where U.S. civilian personnel are the only personnel qualified to make the repairs and the repairs have to be done in Ukraine.
The easiest example I can give is battle damage to an F-16 sufficient to ground the aircraft.
In certain cases, the OEM has the only certified personnel to repair the jet.
Remember the incident when a US Navy EP-3 collided with a Chinese J-8 interceptor?
Although the EP-3 was flyable, China refused to allow the plane to be flown from the island, forcing the U.S. pay to have it dismantled and shipped.
The OEM did most of the work.
There will be situations like that in Ukraine...there needs to be a "legal" way to get the work done.
There will be risks...the personnel who volunteer to do the work will be highly compensated.