First you need to write your MOTD, on Minecraft host, and you can use this website to help you. Once you have your MOTD like you want it, copy the server.properties code in File Manager. like the one shown below
Open your server panel and head to File Explorer. Now, enter your server.properties and head to the motd section and paste the copied text where the old one was, then restart your server and your changes will be made.
How to change your MOTD with ServerListPlus
ServerListPlus is a plugin that changes your MOTD through a plugin also adding features like custom MOTDs for seperate players. You can download it here!
Now download and place the plugin into your servers plugins folder and restart. once you have restarted head, into the ServerListPlus folder and open the config.yml. Now you can change the MOTD how you like. this website can help you make one shown below.
How to change your MOTD with MiniMOTD
ServerListPlus is a plugin (Spigot/Paper/BungeeCord/Velocity) or mod (Fabric/Sponge only) that changes your MOTD using the MiniMessage system and supports RGB (1.16+). You can download it here!
Now download and place the plugin into your servers plugins folder (or mods folder) and restart. once you have restarted head, into the MiniMOTD folder and open the main.conf. Now you can change the MOTD how you like. the MiniMessage docs can help you make one shown below.
MiniMOTD also has some advanced features such as multiple icons per MOTD and different MOTDs per virutal hosts (BungeeCord/Velocity only).
The MiniMessage docs can help you to create the MOTDs and use more advanced features such as gradient colours as MiniMessage works differently to other plugins.
How to change your MOTD on Bungeecord
Changing your MOTD on Bungeecord is slightly different. You can still use ServerListPlus or MiniMOTD, following the guide above, but if you want to do it without ServerListPlus or MiniMOTD, enter your Bungeecord config.yml and head to the MOTD you can use this website to help you like the one below.