using inputbox in the form

i have a tabular form ,
in post_text_item  will check a value if it is exist in the table
otherwise it will insert a record , but it require to receive one value from a user
here is my code

declare
	alert_button number;

begin
		if :V_STAT_D.RESRV is not null then
		if Empl_Exists(:v_emp.emp_no,:V_STAT_D.RESRV) = 0 then  (if record not exist)
alert_button:=show_alert('A_CONF');
if alert_button=alert_button1 then  -- alert asking user to confirm add new record
	-- here we need the form to receive one value from the user
	then insert into 

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is there any way as ms access to send inputbox , the user type in , then use this value to insert into record ?