My suggestion is to double down on what you know already (iOS, swift, etc) and do homework on about 10 companies that pay well and have a need for that skillset. Then, a couple months before your bond gets over, approach these companies and start interviewing. If you are good, you will get at least a couple offers and will be in a good position to negotiate.

Note - the key is to approach these candidate companies more or less in parallel, and not serially. If you have multiple offers, you have a much better chance to make much more than what you are making today, compared to learning a new skill at this point.