In principle, the delivery date specified in the online shop is deemed to have been agreed. The retailer cannot simply change the agreed delivery time unilaterally.
If a specific delivery deadline has been agreed for the online order, the retailer is automatically in default if they fail to meet the agreed delivery date. The safest option is to set a deadline for subsequent delivery anyway.
If you do not want to wait any longer and remain inactive, it makes sense to cancel the online order (if this is not excluded). If you are still interested in a delivery, the customer should first set a deadline for subsequent delivery; if necessary, you can withdraw from the previously concluded purchase contract.
If the retailer allows a grace period for the online order to elapse, the additional costs for a replacement purchase can be claimed by the customer; however, a dispute may arise as to whether the retailer was also responsible for the late delivery.
In individual cases, it is quite possible that the rental costs for a replacement bicycle may have to be reimbursed in the event of a delay in delivery. The decisive factor here is that the constant availability of the bike for personal use must be of central importance and the dealer himself must be at fault for the delayed delivery.