Unfortunately, that’s not possible. There are two conditions that must be met in order for a user to get access to the trial: they must have an active Core membership, and it must be the first time they are activating the trial.
However, feel free to subscribe to Premium for just one month to try it out!
I see that you are having payment issues in this topic (Payment failed while upgrading to $10 plan, and now my $5 membership isn’t working in the AnkiHub add-on - #3 by saad212004). A team member responsible for that will get in touch with you soon.