How to set Length of Custom Field?

I have created a doc type named “Test” and it has 5 fields.
Now I want to change the default length of “data” type from 140 to 10.
It will assign 140 to all field by default but I want to change it.

If anyone knows please help me.
Thanks in advance.

I think you can use the property called “Length” to define the length of column in db.

@nabinhait Thank you for answer but I am not able set the length.
I have tried to set the length but when I click on Update button it will auto reinitialise with 0.

and Also I have tried to change length in DB but when I update the form it will reinitialise with default length of data type.

I could reproduce it. Issue is raised https://github.com/frappe/frappe/issues/6087