Welcome to Adobe.
Please use below prepared form as example for you. it will take the extra text in to the next text field as you requested:
form1.Page1.line1::ready:layout - (JavaScript, client)
// Get the value of the text
var numchar = this.rawValue;
// Slice the text from the 70th character
var numchar2 = numchar.slice(70);
// Replace the sliced characters with the remaining characters
var res = numchar2.replace(numchar2, numchar.slice(70));
// Set the value to the next line
line2.rawValue = res;
// Set the value of the first line to the sliced remaining
this.rawValue = numchar.slice(0,70);