1st up don;t mark as Solution till your happy it does what you want.
Ok 2nd go copy and paste into notepad and save as say getpart.lsp, next find help about running lisp programs. As a start can drag and drop using explorer.
3rd it will select the items based on position you nominate.


You have not said what you want to do with the result the code stores it as a selection set LST, so erase !lst would rub them out.
; simple get objects in using a line selecting by order
; By AlanH June 2021
(defun c:getpart ( / pt1 pt2 ss num)
(setq pt1 (getpoint "\n1st point ")
pt2 (getpoint pt1 "\n2nd point"))
(setq ss (ssget "F" (list pt1 pt2)))
(setq x (sslength ss) inc (getint "\nEnter increment spacing "))
(setq num (fix (/ x inc)) lst '())
(setq start (- inc 1))
(setq lst (ssadd))
(repeat num
(setq lst (ssadd (ssname ss start) lst))
(setq start (+ start inc))
)
(princ)
)
(c:getpart)