Mention it face to face prior to the date starting. Just be cool about it. Like it’s a minor detail. Because to everyone who doesn’t stutter it is minor. But it can get awkward fast when someone doesn’t expect it- i’m sure we’ve all been there. Happens at my job on occasion because you just can’t tell everyone to expect it lol. But a date... sure. My stutter’s never got in the way of dating. Just be cool and confident- tough somes times I guess.