Garmin Gpsmap 7015 custom maps.

Hi.

I have a Gpsmap 7015 installed on my boat. I have been trying to get a map to display on the platter and found this site and have been reading multiple threads regarding.

I get my maps from here Planet.osm extracts | BBBike.org . I have tried both UTF and ascii maps but both say "Map format not supported". I have been using the openseamap format. They claim to have tested it on said device.
I have also tried the patcher found on this site but still no luck. I have recently updated the firmware to version 5.10 or 5.20.

I have also read about version 3.40 successfully loading openseamaps but I am unable to find said version. All the links on this site to version 3.40 is broken.
I'm not sure about a hard reset, I did a "restore to factory settings" and I also tried holding the on button in, it displays garmin logo and the message "holding". But nothing happens after. Is it possible for a download link to version 3.4.

I'm a small commercial fisherman of the coast of Cape Town, South Africa.

Any help would be greatly appreciated.
Thanks.