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What is there about the performance that is not working right?
I'm not sure that changing a setting in that manner (what I can guess about it) will help.
What NMEA2K connected devices do you have interfacing with the HDS Two Touch ?
You may have seemed locked out, if the options could not be changed.
If reception is not good, or GPS performance is not good, unfortunately you may have a defective device. GPS antennas that are internal don't break at all easily, and anything else being wrong with the GPS system than the antenna, would mean 'broken device' most likely.
But one thing: if the device is in an enclosed space, without a clear view of the open sky down to the horizon... if, in sum, the canopy of the boat is metal and blocking GPS satellite signals... then that could be the cause of the problem, too. If so, putting the external GPS antenna out in the open might help with GPS fixes and reception.