Fuel gauge fluctuates at start up

Hello,

This can be due to a faulty fuel level sending unit.
The level sending unit is located in the fuel tank mounted on the fuel pump.
It consists of a float and a resistor panel. As the fuel level goes up and down the float moves and contact to different value of resistance on the panel. This gets translate into the fuel level. If the sending unit is worn it can send incorrect info and the fuel gauge will not show accurate information.

In order to replace that level sending unit the fuel tank needs to be removed.

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.