Can't seem to figure out how to delete several lines from a text file

[Cosmosso]

I want to delete a block of text from a text file that looks like this:

1
Date stored: 2019-02-01;
Author name: l;
Book title: lll;
Quantity: 1;
Price: 2.

2
Date stored: 2019-01-02;
Author name: ghjk;
Book title: okj;
Quantity: 5;
Price: 4.

4
Date stored: 2019-01-02;
Author name: hello;
Book title: hekie;
Quantity: 1;
Price: 2.

1
Date stored: 2019-02-01;
Author name: k;
Book title: k;
Quantity: 4;
Price: 1.

1
Date stored: 2019-01-01;
Author name: o;
Book title: b;
Quantity: 4;
Price: 8.

5
Date stored: 2019-02-01;
Author name: dfgh;
Book title: iuhg;
Quantity: 8;
Price: 4.

But I only want to delete 1 block of text that starts with 1

So I have this code:

from itertools import groupby
    
    mainFileDelete = open("BooksTest.txt","r+")
    
    lst = []
    new = []
    
    for line in mainFileDelete:
        stripped = line.strip("\n")
        lst.append(stripped)
    
    #Makes a list into a list of lists
    def splitList(sequence, delimiter):
        return [list(g) for k, g in groupby(sequence, key = lambda x: x == delimiter) if not k]
    p = splitList(sequence = lst, delimiter = '')
    print(p)
    
    #Gets the sublists that starts with a number '1'
    for k in p:
        this=k
        if this[0] == '1':
            new.append(this)
    print(new)
    
    #Trys to make all of the list of lists into a string an then delete it from 
    #the text file
    for i in new:
        strinng = ''.join(i)
        print(strinng)
        for a in strinng:
            if a != strinng[1]:
                f.write(a)
        f.truncate()
    
    mainFileDelete.close()

It gives me all of the the blocks of text that start with 1 in a list of lists, like so:

[['1', 'Date stored: 2019-02-01; ', 'Author name: l; ', 'Book title: lll; ', 'Quantity: 1; ', 'Price: 2. '], ['1', 'Date stored: 2019-02-01; ', 'Author name: k; ', 'Book title: k; ', 'Quantity: 4; ', 'Price: 1. '], ['1', 'Date stored: 2019-01-01; ', 'Author name: o; ', 'Book title: b; ', 'Quantity: 4; ', 'Price: 8.']]

And I want to delete just the second list from the list of lists. I know how to do it from the actual list. But I don't know how could I also delete it from the file.
I want this one gone from the text file:

1
Date stored: 2019-02-01;
Author name: k;
Book title: k;
Quantity: 4;
Price: 1.

This is the part from the whole code that should do it:

  #Trys to make all of the list of lists into a string an then delete it from 
        #the text file
        for i in new:
            strinng = ''.join(i)
            print(strinng)
            for a in strinng:
                if a != strinng[1]:
                    f.write(a)
            f.truncate()

But it doesn't work at all. Please help. It's the only thing I can't seem to figure out.
Thank you.