Hey, you need to use a job. Go to the jobs tab, from there you can create a job, set your config and wordlist (in addition to proxies and other stuff). You can find some guides on this forum, but I suggest reading the helps from bulletta (the links in blue at the bottom of each section) and she will explain everything to you.
If you need any more info feel free to reply here! I will also leave you another guide which might be helpful if you’ve never used OpenBullet