For you to get the values for the variables:
LET vOBJID = OBJID;
LET vCHANGENR = CHANGENRID;
The above statement will retunr null, because neither OBJID and CHNGENRID are defined.
You must use a peek('FieldName',rowNumber,'TableName') funtion.
CONCAT(Chr(39)&OBJECTID&Chr(39),',') as OBJID
LET vOBJID = peek('OBJID',0,'ObjectID');
LET vCHANGENR = peek('CHANGENR',0,'CDHDR');
this will get some values to your variables
The bolded zero in the peek formula is the number of the row in the data you have, so if you have more than 1 row in your loadeed table, i'll have to figure which one you need.