Hey -
There is a couple of ways to do this but all depends on how much IT skills you have vs time vs money. There is free (to a point) email/user list marketing tools like Mailchimp, Mailgun and other platforms, but you'd need some basic IT skills maybe for them or not, but they aren't bad. Of course CRM's like Hubspot, Salesforce and other things are good for managing customers but they are probably like hitting a peanut with a sledgehammer.
Over the last 16-18 months we have been building functionality like this into The Beauty App, which is free online Salon software. You can use as much functionality in our software for free as you choose, so would be ideal for you just now to store your records if you wanted to give that a try to see if it fitted your needs.
If you want to know more then feel free to DM me (Kim) as I'm the Product Owner and CEO of the company. We did have an iOS app with our original platform however we have completely rewritten I'm a stuit to solely handle cancellations and offers for now, but marketing and customer interaction is on the horizon.
Kim x