How to align some text right to image in wordpress post

You have to align the image to the left. When you’re adding an image in the Attachment display setting select Alignment: Left

i have over 1500 posts , how can i align all images to left automatically?

Use CSS float left
https://www.w3schools.com/css/css_float.asp

E.g;

.post img {
 float: left;
}