【Question 6】
Embed a digit in 1001 to form a five-digit number $10 \square 01$. If this five-digit number is divisible by 7, then the embedded digit “ $\square$ ” is $\qquad$.

 untranslated parts:
- The symbol “$\square$” is used to denote the embedded digit.
- The blank at the end is for the answer to be filled in.
【Analysis and Solution】
Number Theory, Divisibility.
If the five-digit number $\overline{10 \square 01}$ is divisible by 7;

then $\overline{10 \square 01} \times 10=\overline{10 \square 010}$ is divisible by 7;
If the difference between the last three digits and the number formed by the digits before the last three digits of an integer is divisible by 7, then the integer is divisible by 7.
That is, $010-\overline{10 \square}$, then $\overline{10 \square}-10=\overline{9 \square}$ is divisible by 7;
$99 \div 7=14 \cdots \cdots \cdot 1$
$99-1=98$ is divisible by 7;
$98-7=91$ is also divisible by 7;
“ $\square$ ” is 1 or 8.