How do I get and change a value from a mysql database on button click in PHP?

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Javascript

HTML

PHP

All I want is simple: 2 buttons, 1 button gets you a certain value that is in mySQL on click, 2nd button deducts from the value and saves it in mySQL database/updates it.

In an example
mySQL database:
ID 1 Name Textil INT 20
my php page: 2 buttons:
-Get Value
-Change it and Update it

i click Get Value, it gets 20 from textil, then i click change it and update it: and it changes it to a new value i already pre-determined in the script and updates the database.

How do i do this?

What I have tried:

I fond many tutorials but they are all forms like
Name
Surname
Age
and on button click you update the age, and i dont want any input like that, i just want to know how to change a value to an already pre-determined value on button click.