Since you cannot upload a JSON file directly to YouTube, you need a "YouTube Subscriptions Importer" web tool.
Log into your new account in the same browser, open the extension, and upload your .csv file (or use its "collect" feature if you have both accounts logged in). The tool will then automatically "click" subscribe on those channels for you in a background process. Since you cannot upload a JSON file directly
file you just downloaded. The tool will then automatically "click" subscribe on each channel for you in the background. Key Feature Comparison Youtube Subscriptions Transfer - Chrome Web Store file you just downloaded
Here is how to copy your subscribed channels from one account to another. The Fast Way: Using a Subscription Importer The Fast Way: Using a Subscription Importer Most
Most free tools cap out at 500-1,000. For massive accounts, you may need to split the CSV file into two halves and import them in separate sessions.