My approach would look something like this.
First, identify the relationships worth revisiting.
Then review the account history before contacting anyone.
Know who they are.
Know what business they previously did with you.
Know anything important that happened near the end of the relationship.
Next, decide who should make the call.
For an important client, that may be an owner or senior manager rather than someone working from a generic call list.
Then call.
Listen before trying to sell.
If the former client describes a legitimate problem, understand it.
If something needs to be corrected, correct it where possible.
Document what you learn.
And look for patterns across multiple conversations.
Only then does the question of renewed business come into play.
Sometimes the client returns.
Sometimes they don’t.
Either way, the business should know more after the conversation than it did before it.
That’s what makes reactivation more than a sales campaign.