How to pass data from one form to another form?

In the first form, in line 223 I have used an input to get a value from the user.

Then when the user submits the form, there is a second form, and in line 238 I have created a hidden input in which I tried to store the value which I posted from the first form. Then again, this value was posted from the second form to use it later in the code. However, later in the code it seems that no value is being assigned to update_id in line 238. Please tell me what I have done wrong?

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