How to show a long sentence on character LCD by using bascom?
See SPLIT.

You can use e.g. the SPLIT command to split the text in multiple lines (like 0-20 for the first line, 20-39 for the second line, 40-59 for the third line).

However, this is quite a 'crude' way because words will be split in the middle.

To improve this, some smarter algorithm is needed, e.g. checking position 19 if it is a space, if not, go backwards until a space is found, than print index 0 to that position (except the space) to the first line, and do the same for the other two lines. Also it might be there are no spaces at all, or the text will not fit on the three lines (like words of 10 characters each with spaces in between).