In past tense modal verbs are more often used not in the temporary form Perfekt, but in Präteritum. That is, we use not the third form of the verb (“ge” + “-t”) with the auxiliary verb “haben” or “sein”, but the second form of the verb with the suffix (“-te”).
Here are the past tense modal verbs – Präteritum:
Können – konnte;
Dürfen – durfte;
Wollen – wollte;
Sollen – sollte;
Müssen – musste;
The logic here is quite clear: the standard suffix “-te” is added and removed umlaut where it was. As you may have noticed, the modal verbs here are one less. The verb “möchten” is missing, because it is not used in the past tense. The verb “wollen” is used instead.
Endings for conjugation (change in persons and numbers) are as follows:
Ich – wollte;
Du – wolltest;
Er, sie, es – wollte;
Wir – wollten;
Ihr – wolltet;
Sie, Sie – wollten.
Please note that the first and third singular forms do not receive any endings in Präteritum.
Er kann gut Spanisch lesen – he can read Spanish well;
Er konnte gut Spanisch lesen – he could read Spanish well.
Wir möchten ein Kilo Apfel kaufen – we want to buy a kilo of apples;
Wir wollten ein Kilo Apfel kaufen – we wanted to buy a kilo of apples.
By the same principle, the verb “sein” is more commonly used with Präteritum (“war”), and not with Perfekt (“ist gewesen”).
Ich – war;
Du – warst;
Er, sie, es – war;
Wir – waren;
Ihr – wart;
Sie, Sie – waren.
As with modal verbs, the first and third singular forms do not receive any endings in Präteritum.
Ich bin in den USA – I (am) in the USA;
Ich war in den USA – I was in the USA.
It happens that the modal verbs and the verb “sein” are used in Perfekt, but this is much less common.