Even though there are several automatic tools like Jarvee, Followerlike and so on, you will find lots on them in the BHW Marketplace, I would not recommend you to get started with them right away as with the recent updates Instagram has made automation slightly difficult and you would burn your accounts if you're not careful enough.
If they're not too many, stick to sending them manually or hire a VA to do it if it's from just one account.
Or if you really want to go big, keep enough accounts and proxies handy so you're ready at whatever gets thrown at you!