@ultrAslan
There will be a lot of changes and you will need to remove whole Pop Up box.
We need to start from your button in the gallery You need to modify it make sure the Amount is name of Your SharePoint column if not change ThisItem.'NameOfTheAmountColumn'
UpdateContext({varAmount: ThisItem.Amount});UpdateContext({PopUp:true})
You creating a variable called varAmount and Variable PopUp <-- this will control the popup box
To do this we will not use any form delate whole thing and start from schrach to make it easy to explain
Create a container and place all Items in it as on Screen below

We start From TextInput add this control
and Place the code
varAmount
Done ! 😉 joking
Now + and - buttons
First Minus code below will substract and prevent to go below 0
If(varAmount = 0,Notify("Amount cant be les then Zero"),UpdateContext({varAmount:varAmount-1}))
Next Plus button that will just increment
UpdateContext({varAmount:varAmount+1})
And Confirm button now
Replace
TestApp = Your Sharepoint List
Gallery1.Selected.ID = Gallery1 replace with Name of Your Gallery
TextInput2 = name of Your control
Patch(TestApp,
{ID:Gallery1.Selected.ID},
{
Amount:Value(TextInput2.Text)
}
);
UpdateContext({PopUp:false})
Cancel button
UpdateContext({PopUp:false})
You should have something like that now

make it pritty like before 🙂
and in the Container Visible property place
PopUp
Let me know if something go wrongin case of error make a screen and write the error to allow me to help find what cause it