Metroidvanias are known for their gameplay in which you must collect upgrades and power-ups to progress through the game. Metroid Dread is a prime example of this genre and features numerous ways players can improve Samus' arsenal. One of these is the Super Missile.
To unlock the Super Missile, you will need to travel to the southern end of Ghavoran. From the Dairon elevator, head left and cross through the first room. After entering the second room, use a bomb to reveal a secret passageway just beyond the door into that room. Follow this path.
You will soon arrive at a Chozo Statue holding a power-up. Break it to unlock the Super Missile. This is an upgrade that increases the power of your missile as well as lets you break green missile door domes. With this upgrade, you can backtrack to previously barred pathways and explore them.
The upgraded damage from the Super Missile is also a huge plus as you can take out enemies and bosses quicker. You don't have to do any extra to fire a Super Missile as all of your standard missiles will be the upgraded version. Simply hold R and press Y to fire Super Missiles as you would normally.
For more information on Metroid Dread, check out How to Access Domed Doors in Metroid Dread and How to get the Grapple Beam and Bombs early in Metroid Dead – Sequence Breaking on Pro Game Guides.