You don’t really want to do mobile appoints just for a tint and shape, so what else would that client book for? Would they have a pedi or some body waxing? Get that booking for their patch test visit and return to do the tint
Make sure every client gets patch tested when they have their first appointment so that they have more options in future.
What I suggest you do is prompt your clients to book a brow shape as a “would you like anything else” upgrade to their booking. Then patch test so they can add a tint next time, Redo every 6 months (if they haven’t had a tint) and that gives you a chance to talk about how great the tint would be for them.
It’s better to proactively manage bookings that require a patch test and build the business that works for you. I refuse to do brow shaping unless it’s booked with another service, so when I upsell a tint I already have a decent client booking.