You should consult your physician who has prescribed you the injection. If he /she suspects that injectible route is better for replenishment of your
B12 deficiency ( which might be the case , if you are having gut absorption issues) , it would be wiser to take the Injection and not shift to the oral format.
In this medicine the absorption of the drug via an injection and via oral route varies a lot. The decision has to be taken by your consultant , keeping your health issues as the foremost priority.