Add `datadir=<full path to custom datadir>` on the first line of the Blockmarket syscoin.conf file

Windows: C:\Users\[USERNAME]\AppData\Roaming\Blockmarket\

MacOS: /Users/[USERNAME]/Library/Application Support/Blockmarket/


And then restart Blockmarket


Syscoin Blockmarket core will then look to the custom datadir for wallet.dat and blockchain data.