Hey @kinokritik ,
To change the location of where line items from an Order will be fulfilled from, if you are using API Version 2019-10 an above, you need to use the Fulfillment Order resource. You can read more about it here: https://shopify.dev/tutorials/manage-fulfillments-with-fulfillment-and-fulfillmentorder-resources
So in a nutshell in GraphQL API you need to use the mutation fulfillmentOrderMove https://shopify.dev/docs/admin-api/graphql/reference/mutation/fulfillmentordermove to change the fulfillment order (e.g. the group of line items being fulfilled together https://shopify.dev/docs/admin-api/graphql/reference/object/fulfillmentorder) to a new location ID