Please, refer apoc.create.setRelProperty documentation
Attributes are Key Value pairs.
A small demo
data.csv
col1,col2,col3,col4,col5
T1,TA1,T1TA1,Medium,4
T2,TA2,T2TA2,High,5
T3,TA3,T3TA3,Low,3
T4,TA4,T4TA4,Moderate,2
T5,TA5,T5TA5,Very Low,1
USING PERIODIC COMMIT 100 load csv with headers from 'file:///data.csv' as row
with row where row.col1 is not null
merge (c1:Col1 {id: row.col1})
merge (c2:Col2 {id: row.col2})
merge (c1)-[r:HAS]->(c2)
with r,c1,c2,row
CALL apoc.create.setRelProperty(r, row.col4, row.col5)
YIELD rel
return c1,r,c2;
βββββββββββββ€βββββββββββββββββ€βββββββββββββ
β"c1" β"r" β"c2" β
βββββββββββββͺβββββββββββββββββͺβββββββββββββ‘
β{"id":"T1"}β{"Medium":"4"} β{"id":"TA1"}β
βββββββββββββΌβββββββββββββββββΌβββββββββββββ€
β{"id":"T2"}β{"High":"5"} β{"id":"TA2"}β
βββββββββββββΌβββββββββββββββββΌβββββββββββββ€
β{"id":"T3"}β{"Low":"3"} β{"id":"TA3"}β
βββββββββββββΌβββββββββββββββββΌβββββββββββββ€
β{"id":"T4"}β{"Moderate":"2"}β{"id":"TA4"}β
βββββββββββββΌβββββββββββββββββΌβββββββββββββ€
β{"id":"T5"}β{"Very Low":"1"}β{"id":"TA5"}β
βββββββββββββ΄βββββββββββββββββ΄βββββββββββββ