The shop's withdrawal policy contains the applicable conditions, time limits and return costs: https://gemashop.de/policies/refund-policy
Submit an unambiguous declaration using the route described there or https://gemashop.de/apps/omnibus/withdraw. Using the form is not a requirement for a valid withdrawal declaration.
For return arrangements, email support@gema-net.de with order number and product. Heavy-item transport is discussed individually. Contacting support does not replace or extend statutory time limits.
Return address, cost responsibility, collection and refund timing depend on the case and applicable conditions. Additional prior approval is not a requirement for exercising an existing withdrawal right.