The first step in this process is finding the blacklisted email address(es) that you want change in the EMAILINVALIDRECIPIENT table using a select statement such as:
 
select * from EMAILINVALIDRECIPIENT
where address = 'example@email.com'
 
And then changing the isblacklisted value using the following script:
 
update EMAILINVALIDRECIPIENT
set isblacklisted='0'
where address = 'example@email.com'

If you want the email address to be blacklisted, change the value to 1. If you want to unblacklist the email address, change the value to 0.