When you want to harvest your crops and go to the Market to sell them in exchange for Seeds, you can simply tap on the Market icon.
And then confirm by tapping on Harvest Now.
If you've just recently planted crops on six different plots to unlock the Market Day, there's a 24 hour cooldown before the Market opens and you can use harvest your crops. You can skip this cooldown by tapping the View to Start Now! button and watching a short ad.
