According to Realme's initial roadmap for Android 10, the Realme 3 and Realme 3i are due to get the update in April and now, the company has opened up its beta programme for these two phones. Realme 3 and 3i users have option to join the Realme UI open beta programme, for a first-hand feel of Realme UI, based on Android 10. The company's blog post cautions users that there would be bugs and minor issues in the beta version, so proceed only if you're willing to take this risk. A backup of all your important data is also recommended as you won't be able to roll back to the stable ROM after the update. There are also limited slots, so if you don't get the option to join, then you'll have to wait for the final version. If you still wish to proceed, here's what you need to do.
One of the most important things, according to the company's post, is to make sure you're on the latest version of ColorOS. For the Realme 3 (Review), it's RMX1821EX_11.A.28 and for the Realme 3i (Review), it's RMX1827EX_11.A.28. In case your phone is not on these versions, then you can manually download and update it from here. Realme also recommends a phone battery level of more than 60 percent and you should have more than 5GB of free space available.
If you've done everything right, then go to Settings > Software Update > Click the top right button > Tap Trial Version. You should see ‘realme UI Open Beta- realme' here. Tap this and the update should begin downloading.
Realme recommends updating all your apps before joining the beta as there may be some instances of incompatibility. After the update, you might encounter some common issues such as a longer boot time, right after the update and slightly sluggish performance for a brief moment the first time it boots in to Realme UI. There's another known issue where if you try and unlock the 3 or 3i on the beta ROM under strong light, it might cause a black screen. This issue would be rectified in the final version, according to Realme.