How to block, mark as spam, or unblock phone numbers on Realme devices

Realme 5 Pro Realme 5 Pro
Realme Q Realme Q
Realme 3i Realme 3i
Realme C1 (2019) Realme C1 (2019)
Realme 3 MT6771 Realme 3 MT6771
Realme X Lite Realme X Lite
Realme X Master Edition Realme X Master Edition
Realme X Realme X
Realme 3 Pro Realme 3 Pro
Realme C2 Realme C2
Realme 3 Realme 3
Realme U1 Realme U1
Realme 2 Pro Realme 2 Pro
Realme C1 Realme C1
Realme 2 Realme 2
Realme 1 Realme 1