I'm assuming you're coming from Mycelium, Electrum, Bread wallet, or some other software that had you write down as 12 word "Wallet Seed Recovery Phrase." This phrase can be called a "Mnemonic Backup" or "BIP39." It should look like twelve random words. You'll need those words to continue with this guide.
Once you've downloaded and installed the software, read the introduction, and wrote down your new 12 word phrase you're ready to begin importing your old wallet. Remember, you MUST SET UP A NEW WALLET FIRST.
If you want to use this software for BTC and BCH you will need to follow these steps for both the Bitcoin Cash blockchain and the Bitcoin Core (formerly Bitcoin) wallet.
- Click the + icon next to the blockchain you wish to import.
- Click 'Create New Wallet.'
- Enter a name for this wallet (Such as "Old Wallet") and then click 'Show advanced options.'
- Click the dropdown next to 'Wallet Key.' Change the value from 'Random' to 'Specify Recovery Phrase.'
- Enter your recovery phrase from the old wallet in the field marked 'Wallet Recovery Phrase.' Click 'Create new wallet.'
- Now the Bitcoin.com wallet is aware of your old account, but it still shows 0 balance. To correct this click 'Settings' in the bottom right and then 'More Options.'
- Click 'Wallet Addresses' and then 'Scan addresses for funds.' This may take several minutes, but once complete you should see your balances have updated.
- I recommend moving the funds from your old addresses to your new, then deleting the old. It's tidier. But you do you.