Certificate expired can it be renewed remotely

[mylaps]

We have some remote units which open up a VPN port to our office.
This has been working for a few years but now the remote units can not be connected anymore.
Looking at the error we found out the certificates on the remote units are expired.
Can these be renewed from our office or does this need to be done at the remote location

[doktornotor]

You have some other access except via VPN? If not, pretty much tough cookies.