⭐ Merited by apogio (1)
A brief instruction can be helpful. 
That one command Loyce has provided before your reply is all you need.Everything that could conflict are already pre-configured to use separate/different values by default.
For more simpler guide (if you're on Windows), check this thread in 'Beginners & Help' board: /index.php?topic=5215716.0#post_actsteps
Note: --testnet is for "testnet3", --testnet4 is for the latest testnet, there's also --regtest for other tests that can be done locally.
Code:
{
"chain": "testnet4",
"blocks": 0,
"headers": 0,
"bestblockhash": "00000000da84f2bafbbc53dee25a72ae507ff4914b867c565be350b0da8bf043",
"bits": "1d00ffff",
"target": "00000000ffff0000000000000000000000000000000000000000000000000000",
"difficulty": 1,
"time": 1714777860,
"mediantime": 1714777860,
"verificationprogress": 3.93201064047899e-08,
"initialblockdownload": true,
"chainwork": "0000000000000000000000000000000000000000000000000000000100010001",
"size_on_disk": 269,
"pruned": false,
"warnings": [
]
}
"chain": "testnet4",
"blocks": 0,
"headers": 0,
"bestblockhash": "00000000da84f2bafbbc53dee25a72ae507ff4914b867c565be350b0da8bf043",
"bits": "1d00ffff",
"target": "00000000ffff0000000000000000000000000000000000000000000000000000",
"difficulty": 1,
"time": 1714777860,
"mediantime": 1714777860,
"verificationprogress": 3.93201064047899e-08,
"initialblockdownload": true,
"chainwork": "0000000000000000000000000000000000000000000000000000000100010001",
"size_on_disk": 269,
"pruned": false,
"warnings": [
]
}
It started with 1 year 14 weeks behind, hope I am doing it the right way.