The next step is for your dog to keep touching your hand with their nose for a little longer. Encourage them to do this by waiting slightly, just a second to begin with, when they make contact with you before marking and rewarding them. Once your dog is consistently keeping their nose on your hand for one second before hearing the marker word and getting their treat, hold on a little longer still, so for two seconds now, before saying the marker word and giving the treat. Repeat every small step several times, so your dog can be confident that to keep touching you is what you want, and then very gradually use this technique to slowly increase the length of time they will remain touching you for!
When your dog can reliably wait for five seconds while touching your hand with their nose, introduce a very slight distraction, for instance hold a bit of kibble or a toy (but not their favourite, don’t make it too hard!) in your other hand. Hold your target hand out and ask for the “touch”, and if they touch your hand with the distraction present, mark and reward with an extra tasty treat.
Now you can try practicing in different places but be prepared to repeat some of the early steps while your dog adjusts to all the distractions of the great outdoors! Remember, the more distractions around, the harder it might be for your dog, so keep sessions short and fun with lots of tasty treat rewards.