If you need to get funds from Harmony to Polygon, the best way to do so currently seems to be the Synapse bridge.
Before you start, make sure you add Polygon to MetaMask.
First, convert your funds to USDC on Harmony using Sushiswap (the bridge doesn’t directly support MATIC from Harmony it seems, though I could be wrong).
Then, follow these steps:
Step 1: Go to the Synapse bridge
Choose Harmony for “From” and Polygon for “To”.
Choose the token type and amounts you want to send (be sure to double check the amounts of USDC you’ll need for conversion to MATIC, as the price changes frequently).
Once you’ve double-checked all details, click the bridge token button to confirm, sign it with metamask, and wait for the transaction to process.
Simple enough. Same steps for your initial trade, but make sure your MetaMask network is now Polygon.