Hi Luke,
Your old TOMO was automatically converted to TOMO native as TomoChain mainnet was launched in Dec 2018. You needn’t do anything. Just switch to TomoChain network on Metamask. You will see your TOMO balance.
If this is the first time you enter TomoChain mainnet on Metamask, please make sure your Metamask was connected to TomoChain network.
Follow this instruction to add TomoChain network..
Let me know if you get any troubles.
Cheers,
Tam.