By using db<>fiddle, you agree to license everything you submit by Creative Commons CC0.
create table tcharacter (
id int not null,
[create date] datetime2(3) not null,
[mode] varchar(10) not null
)
create table titem (
[type] varchar(10) null,
[Attr] varchar(10) not null,
[char_ID] int not null
)
UPDATE x
SET x.type= 'newid'
FROM Titem AS x
INNER JOIN TCharacter AS y ON x.char_id = y.id
INNER JOIN Titem AS z ON z.char_id = y.id
WHERE x.type = 'oldid'
and z.type = '2nd id'