I'd probably create an active list so you can see all of those contacts from the companies at once. You'd just have to determine the criteria that puts them on the list. It sounds like the new companies were uploaded manually, so maybe use create date and offline source, unless there's something else that would identify them.
After you have that list, you can then bulk enroll the contacts into the sequence using the checkbox and enroll in sequence option.
I'd probably create an active list so you can see all of those contacts from the companies at once. You'd just have to determine the criteria that puts them on the list. It sounds like the new companies were uploaded manually, so maybe use create date and offline source, unless there's something else that would identify them.
After you have that list, you can then bulk enroll the contacts into the sequence using the checkbox and enroll in sequence option.