How to get substring in SQLIte?

Use the substr function.

From the list of core functions:

substr(X,Y,Z) substr(X,Y) substring(X,Y,Z) substring(X,Y)

The substr(X,Y,Z) function returns a substring of input string X that
begins with the Y-th character and which is Z characters long. If Z is
omitted then substr(X,Y) returns all characters through the end of the
string X beginning with the Y-th. The left-most character of X is
number 1. If Y is negative then the first character of the substring
is found by counting from the right rather than the left. If Z is
negative then the abs(Z) characters preceding the Y-th character are
returned. If X is a string then characters indices refer to actual
UTF-8 characters. If X is a BLOB then the indices refer to bytes.

substring() is an alias for substr() beginning with SQLite version
3.34.