Today I am going you to share another blog related to Search configuration on site collection. The shared Search Box at the top of most pages will use these search settings. Any settings you specify on site collection level will apply to all sites within that site collection, unless you specify other settings for a particular site.
How can create search result page for site collection:
1- Go to Search site collection from “SharePoint Admin Center” – Site collection
2- Open Search Url (/search) in browser.
3- Click on 
from right and select “Site Content”.
4- Click on “Pages” app from Site content page as shown in image below.
5- Click on “New” and select “Page” from pop-up
Enter following details:
A- Title and Url name (It will automatically get populated and it can be changed if applicable)
A.1- Select “(Welcome Page) Search results” page layout and click Create
B- User will be redirected to Page library and you can see newly created “Search result page”
C- Select Newly created Search page and go to ribbon
D- Select “Major version (publish)” and click ok as shown below in screen shot.
How We Can Configure Site collection Search result page:
1- Go to Tenant site collection url from “SharePoint Admin Center” – Site
2- Open Site Url (https:///sites/Dev ) in browser
3- Click on from right and select “Site Settings”
4- Go to “Site Collection Administration” section and click on “Search Settings”
5- Update below settings, put newly created page URL.
6- (https:///search/Pages/DevResult.aspx ) at “Result Page Url:”