Sure, I can help you with that. Unfortunately, Roku doesn't natively support the m3u format, but you can use a third-party channel that does. Here's how you can do it using the M3U Black Player:

1. Go to the Roku web site, sign in to your account you have linked with your Roku device.

2. Click on 'Add Channel with a code' under 'Manage Account'.

3. Enter the code 'M3UBLACK' and select 'Add Channel'.

4. You will receive a warning, continue to proceed.

5. The channel will not immediately appear on your Roku device, you have to force an update by going to Settings > System > System Update > Check Now on the device.

6. Once the channel is installed, you can open it from your Roku device.

7. You will see a URL and an activation code on the screen.

8. Go to the URL on your computer or mobile device, input the code, then upload your M3U playlist file or enter the M3U playlist URL.

9. Once you have added your playlist, you should be able to access it from the M3U Black player on your Roku device.

Please note that the M3U Black player is a private Roku channel. Private channels are not officially supported by Roku and are created by independent developers. Use them at your own risk.