A movement is operated manually by the stem, which is usually screwed into the crown. The Seiko movements sold here, have one stem added to the package. But sometimes you need a stem, so here is the place to order it.
Making the stem the correct length is tricky, I suggest buying two stems so you have room for error on the first.

7S26 stem fits: 7S26, 7S25, 7S36, 7S35, 4R15, 4R16 (also Pulsar Y674, Y675, Y676).

4R36 stem fits: 4R36, 4R35, 4R34, 4R37, 4R38, 4R39, 4R57, 4R71, 6R15, 6R20, 6R21, 6R27, 6R31, 6R35, 6R64, 8R28, 8R46, 8R48 (probably all movements 4Rxx, 6Rxx, 8Rxx).

Seiko diver crowns have a system that clicks the crown into a construction with a spring. So the stem can move a bit up and down. I have not been able to remove or replace such a stem. So with a diver, you have to replce the crown complete. Most after-market replacement crowns have the spring system and the stem can be crewed into the crown.