Once a membership has been cancelled, that member will be directed to the general Cobot login page, without being an active member in any space. You have two options to bring them back in as members of your space:
1) Reactivate Your Member's Account And Change Their Plan In Your Admin Area.
This method will have you reactivate their membership so that they will be re-registered when they log in.
Find their name under Manage » Members » Cancelled Members.
Click the drop-down menu by Plan » Customize Plan or Change Plan to either change completely or make edits to their existing plan. You can edit the membership fees, etc. You can also edit their next renewal date under the Membership box, and make any other changes needed prior to re-activating their membership.
Once you are happy that everything is correct, go to Membership » Undo Cancellation.
2) Have The Member Sign Up For A NewPlan On Their Own.
Send them a link to the plan, which can be found under Setup » Plans » copy plan link
Have the member follow the link and then sign in to Cobot using their existing login details.
Now they can register as usual and choose their own activation date.